After a borehole has been formed into the earth and cased, it is necessary to communicate the hydrocarbon bearing formation through which the well bore extends with the interior of the casing so that production fluid can flow uphole to the surface of the earth. There are deep wells exceeding 15,000 feet in depth which have extremely high temperature gradients as measured from near the surface of the earth to the bottom of the borehole. The temperature at the production formation often exceeds 400.degree. F. For this reason some tool strings must be run into proximity of the bottom of the borehole with great caution, otherwise, the excessive temperature will bring about deleterious effects to some components thereof.
This is especially so with jet perforating apparatus for the obvious reason that the various components thereof cannot endure such an elevated temperature. More importantly, the electrical and explosive apparatus associated with the circuitry cannot endure this temperature. The explosives become ultrasensitive and change in chemical composition at these excessive temperatures.
Others have attempted to employ special high temperature explosive material and devices which can endure for a while at elevated temperatures; however, it is much preferable to utilize well known explosive apparatus, circuitry, devices, and techniques wherever it is possible, thereby taking advantage of years of accumulated knowledge.